The Project host has shocked her co-panellists after she revealed she and her family engage in an unsavoury practice.
The conversation came after comedian Sarah Silverman told hosts of US talk show The View she shares a toothbrush with her partner Rory Albanese.
After sharing a clip of the interview, Lisa said, "That's so gross, that's so gross", before Kate hit back, "Is is? Why is it gross?"
Peter agreed the act was disturbing, and said: "It is mouth stuff."
"There is kissing that goes on, but that's a separate issue. You get really in there. You do it as well, do you?" he asked Waleed.
He admitted he would share a toothbrush if he left it in the downstairs bathroom.
"You're too lazy to walk downstairs?" Peter quizzed.
"Yes," Waleed replied.
"Get your steps up and do your mouth a favour," Peter clapped back.
Kate then admitted she and he husband Peter routinely share the same toothbrush.
"We drifted into it. Now the whole family ...," she said, before Lisa replied, "Stop, don't go there!"
Kate went on to add they had a communal cup in the bathroom.
"We've technically got enough toothbrushes for everyone, but not the will to allocate colours," she said.
"Just pick a random one. Sometimes I go, 'That's a bit shaggy'."
Peter then disturbed the crowd when he asked what happened when they ran out of dental floss.
"They just use each other's fingernails, where do you draw the line?" he asked, before Kate said, "I don't know what goes on in your relationship".
Kate has three children, three of whom are boys, and Lisa claimed boys did not have the same dental hygiene.
"Look, I don't know ... it is clean ... it is," Kate responded.
"The whole point of a toothbrush is to get in there and get rid of the yuck," Lisa replied.
Sharing a toothbrush appears to be a controversial topic, with many of The View hosts disturbed when Sarah Silverman first made the revelation.
Fans of the show described it as "bizarre" and "gross".
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